just to add to what Lil said - i didn't find my colonocopy too bad. The prep was okay - you just have to put up with some D before hand, in actual fact this D was better than the normal type i have, normally it is 'explosive' or at least caught up with some wind, but with the prep it was quite painless.
The test itself is pretty okay, you should be quite well sedated and shoudn't remember too much of the details.
Of course everyone is different and reacts differently to things - i can understand you being anxious with what happened to your father. But the chance of something going wrong is very slim, and by the sounds of your symptoms perhaps it would be a good idea to have it done.
Hope you find some answers tho and keep posting!